US6650801B1 - Reversible optical circulator utilizing a bi-morphic piezoelectric apparatus - Google Patents

Abstract

A reversible optical circulator has an optical switch that includes: an arm composed of piezoelectric material with first and second faces and first and second ends, an electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm, a support coupled to the first end of the arm for fixedly supporting the first end, an object with a convex surface coupled to the second end of the arm, a polarization rotation element coupled to the second face of the arm, a first magnet proximately located to the object and the first face of the arm, and a second magnet proximately located to the object and the second face of the arm. By using this optical switch, the optical circulator has stable and reproducible operation, high switching speeds, and low sensitivity to slight optical mis-alignments.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a DIVISIONAL of U.S. Patent Application titled, “Method And Apparatus For Optical Switching Devices Utilizing A Bi-Morphic Piezoelectric Apparatus”, Ser. No. 09/513,777, filed on Feb. 24, 2000 now U.S. Pat. No. 6,463,189.

FIELD OF THE INVENTION

The present invention relates to optical devices, and more particularly to optical switching and routing devices.

BACKGROUND OF THE INVENTION

The use of optical fiber for long-distance transmission of voice and/or data is now common. As the demand for data carrying capacity continues to increase, there is a continuing need to utilize the bandwidth of existing fiber-optic cable more efficiently. An established method for increasing the carrying capacity of existing fiber cable is Wavelength Division Multiplexing (WDM) in which multiple information channels are independently transmitted over the same fiber using multiple wavelengths of light. In this practice, each light-wave-propagated information channel corresponds to light within a specific wavelength range or “band.”

Because of the increased network traffic resulting from the use of the WDM technique, there is an increasing need for sophisticated optical switching and routing devices which can quickly route numerous channels among various optical communications lines and which can reliably divert network traffic to alternative routes in the event of network failures. Routine network traffic routing requires optical switching devices that can perform reproducibly over many thousands of switching operations. Network failure restoration requires a switching device that must instantaneously perform according to specification after long periods of non-use. The present invention addresses these needs.

SUMMARY OF THE INVENTION

A reversible optical circulator has an optical switch that includes: an arm composed of piezoelectric material with first and second faces and first and second ends, an electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm, a support coupled to the first end of the arm for fixedly supporting the first end, an object with a convex surface coupled to the second end of the arm, a polarization rotation element coupled to the second face of the arm, a first magnet proximately located to the object and the first face of the arm, and a second magnet proximately located to the object and the second face of the arm. By using this optical switch, the optical circulator has stable and reproducible operation, high switching speeds, and low sensitivity to slight optical mis-alignments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1aand1bare side and top views, respectively, of a first preferred embodiment of a bimorphic piezoelectric deflection and latching apparatus in accordance with the present invention.

FIG. 1cillustrates a second preferred embodiment of a bimorphic piezoelectric deflection and latching apparatus in accordance with the present invention.

FIGS. 2aand2bare side views of the two stable operating positions of the second preferred embodiment of the bimorphic piezoelectric optical switch in accordance with the present invention.

FIGS. 3aand3billustrate a first preferred embodiment of an optical switch in accordance with the present invention.

FIG. 3cis a diagram of the optical pathway of a signal or composite signal through the glass prism in accordance with the present invention.

FIG. 3dis a graph of total deflection and difference between incidence and exit angles through the glass prism of the optical switch in accordance with the present invention.

FIG. 4aillustrates a second preferred embodiment of an optical switch in accordance with the present invention.

FIGS. 4band4cillustrate two alternative dispositions of the optically slow direction and optically fast direction of a half-wave plate in the differential phase retardance switch in accordance with the present invention.

FIGS. 5aand5billustrate a third and a fourth preferred embodiment of an optical switch in accordance with the present invention.

FIGS. 6a,6band6care, respectively, a side view, a top view and an end view of a preferred embodiment of a reversible circulator in accordance the present invention.

FIG. 7 is an end view of the port configuration of the input and output ports of the reversible circulator in accordance with the present invention.

FIGS. 8 and 9 are sequences of cross sections through the preferred embodiment of the reversible circulator in accordance with the present invention.

FIG. 10aillustrates the operation of a conventional 4-port optical circulator.

FIG. 10billustrates the operation of a preferred embodiment of a reversible circulator in accordance with the present invention.

FIGS. 11a,11band11care, respectively, a side view, a top view and an end view of a preferred embodiment of a switchable optical channel separator in accordance the present invention.

FIGS. 12-15 are sequences of cross sections through the preferred embodiment of the switchable optical channel separator in accordance with the present invention.

FIGS. 16aand16billustrate two operational states of the switchable optical channel separator in accordance with the present invention.

FIG. 17 is an illustration of a preferred embodiment of a self-switching optical line restoration switch in accordance with the present invention.

FIG. 18 is an illustration of a preferred embodiment of an optical bypass switch in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides method and apparatus for optical switching devices utilizing a bi-morphic piezoelectric apparatus. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.

To more particularly describe the features of the present invention, please refer to FIGS. 1 through 18 in conjunction with the discussion below.

FIGS. 1aand1bare side and top views, respectively, of a first preferredembodiment100 of a bimorphic piezoelectric deflection and latching apparatus in accordance with the present invention. Theapparatus100 comprises two elongate plates102a-102bcomprised of a piezoelectric material such as quartz and securely bonded in parallel to one another and mounted insupport members104aand104b. Afirst electrode101ais disposed between the piezoelectric plates102a-102balong their bonded faces. Also, a second101band a third101celectrode is disposed along the side of the first102aand the second102bplate opposite to its bonded face. When so bonded and mounted, the pair of piezoelectric plates102a-102bcomprise asingle cantilever arm103 comprised of afirst end103a, which is rigidly physically supported by support elements104a-104b, and a second opposing “free”end103bwhich is not permanently physically mounted. Disposed to either side of thefree end103bofcantilever arm103 are a first110aand second110bpermanent magnet. Also, a solid object with a roundedconvex surface108, such as a metallic sphere or spheroid, is mounted at thefree end103bofcantilever arm103. The metallic sphere orspheroid108 is comprised of a material such as iron, steel, or nickel that experiences a magnetic force of attraction towards eitherpermanent magnet110aor110b. Finally, anoptical element106, such as a glass prism, is mounted tocantilever arm103 along a free length of thearm103 near themetallic sphere108.

FIG. 1cillustrates a secondpreferred embodiment150 of the bimorphic piezoelectric deflection and latching apparatus in accordance with the present invention. In theapparatus150, thesingle sphere108 is replaced by a pair of opposinghemispheres108a-108b, where the firstmetallic hemisphere108ais mounted on thefirst plate102aat thefree end103bofarm103 so as to face thefirst magnet110a, and the secondmetallic hemisphere108bis mounted on thesecond plate102bat thefree end103bofarm103 so as to face thesecond magnet110b. The operation ofapparatus150 is not significantly different from that ofapparatus100 described above.

When at rest precisely between the two magnets110a-110b, as shown in FIG. 1a, thefree end103bofcantilever arm103 is in a hypothetical metastable physical state since the upward force of attraction between sphere orspheroid108 and thefirst magnet110aexactly balances the downward force of attraction between sphere orspheroid108 and thesecond magnet110b. However, such an intermediate metastable state cannot physically exist for any finite period of time because slight perturbations of the position of thearm103 will create situations in which the upward and downward magnetic forces are unbalanced and where thefree end103bofarm103 will either be pulled upward until sphere/spheroid108 comes into contact with thefirst magnet110aor else will be pulled downward until sphere/spheroid108 comes into contact with thesecond magnet110b. These two alternative positions comprise a pair of stable, “latched” positions.

In operation, differential voltages are placed across the faces of the two bonded piezoelectric plates102a-102bvia the electrode101a-101csuch that the resulting differential piezoelectric expansion and/or contraction causes flexure of thecantilever arm103.Electrode101bmaintains a constant voltage andelectrode101cis electrically grounded. A variable signal voltage is applied to thecentral electrode101aso as to create the differential voltages across the two piezoelectric plates102a-102b. The direction of flexure forcantilever arm103 is controlled by the magnitude of the signal voltage onelectrode101aand can be either upward or downward. Because support members104a-104brigidly support thefirst end103aofcantilever arm103, all such flexure is taken up by thesecond end103bofarm103 disposed between magnets110a-110b. By this means, it is possible to achieve precise, rapid and reproducible bi-stable control of the deflection of thesecond end103bofcantilever arm103, and, more particularly, of the position of theprism106. As shown in FIG. 2a, whenapparatus150 is in the upward latched position or “off” state,prism106 does not intercept anoptical signal202. However, as shown in FIG. 2b, whenapparatus150 is in the downward latched position or “on” state,prism106 is disposed so as to intercept, and thereby deflect, theoptical signal202.

FIGS. 3aand3billustrate a first preferred embodiment of an optical switch which utilizes the deflection and latching apparatus in accordance with the present invention. Thisoptical switch300 is a 1×2 optical switch. FIG. 3aillustrates the “off” switch position in whichapparatus150 is latched in its upward state such thatprism106 does not intercept signal light pathways. Conversely, FIG. 3billustrates the “on” switch position in whichapparatus150 is latched in its downward state such thatprism106 intercepts signal light pathways. In both FIG. 3aand FIG. 3b, an optical signal or compositeoptical signal202 emanates from aninput fiber302 and is collimated by acollimating lens303 so that the resulting collimated light beam crosses the “on” position ofprism106. As shown in FIG. 3a, with theswitch300 in the “off” state, the optical signal or compositeoptical signal202 passes in a straight line past the position ofapparatus150 so as to be intercepted by focusinglens305aand thereby focused intofirst output fiber304a. However, with theswitch300 latched in the “on” state, as shown in FIG. 3b, the signal orcomposite signal202 intercepts theprism106 and is thereby deflected from a straight line path. The deflection is such that the signal orcomposite signal202 is intercepted by focusinglens305band thereby focused intosecond output fiber304b.

FIG. 3cis a diagram of the optical pathway of a signal orcomposite signal202 through theglass prism106 of theoptical switch300 in accordance with the present invention. The angle φ₁is the angle of incidence, with respect to the surface normal to the entrance face ofprism106, ofsignal202 upon theprism106 and the angle φ₂is the exit angle, with respect to the surface normal to the exit face ofprism106, ofsignal202 upon leaving theprism106.

For maximum stability of the output ray path against slight angular mis-alignments or vibrations, the angle δ between the projections of the incoming and outgoing segments ofsignal202 must vary as little as possible with the angle of incidence φ₁. This condition is true when δ is at a minimum value and, consequently, when the sum φ₁+φ₂is at a minimum value. Simple geometric analysis shows that this condition is true when the angle of incidence φ₁is chosen such that φ₁=φ₂. FIG. 3dis a graph of δ and φ₂−φ₁versus φ₁showing that, for a typical prism, the minimum in δ occurs when the incidence and exit angles are identical. The stability and reproducibility of the preferred embodiment is greatest with such a configuration.

FIG. 4aillustrates a second preferred embodiment of an optical switch in accordance with the present invention. The second preferred embodiment is a differential phase retardance switch180 which is based upon the bimorphic piezoelectric deflection and latchingapparatus150, described above. In theswitch180, instead of a prism, an optical half-wave plate186 is mounted to thearm103. When theswitch180 is in its “off” position, the half-wave plate186 is not in the path of an optical signal or beam. When theswitch180 is in its “on” position, however, the half-wave plate186 is disposed so as to intercept the path of an optical signal or beam and to be in a particular optical orientation. Other aspects of the operation of theswitch180 are similar to those ofapparatus150. The differential phase retardance switch180 may be utilized in complex switching devices as subsequently described herein in more detail.

FIG. 4band FIG. 4cillustrate two alternative dispositions of the opticallyslow direction188aand opticallyfast direction188bof half-wave plate186 in theswitch180 in accordance with the present invention. The ellipses in FIGS. 4band4care representations of the refractive indices experienced by plane polarized light passing throughplate186 with a variety of polarization plane orientations. The orientations ofdirection188aanddirection188bmay be interchanged—that isplate186 may be rotated by 90°—in the configuration of either FIG. 4bor FIG. 4cwithout changing the operation of the differentialphase retardance switch180. In FIGS. 4band4c, theangle α190 represents the rotation angle that theplate186 undergoes during rotation of theswitch180 from its latched “off” to its latched “on” position. The orientation of either thefast direction188bor theslow direction188aof half-wave plate186 makes anangle β192 with the horizontal whenapparatus180 is in the “off” position. In the preferred configuration illustrated in FIGS. 4b-4c, theangle190 comprises the angle between the base ofplate186 and the horizontal, but this need not be the case.

The configuration illustrated in FIG. 4bis such that the slow and fast directions of half-wave plate186 are disposed horizontal and vertical, or vice versa, whenswitch180 is in its “on” position and half-wave plate186 is disposed so as to intercept an optical path. The configuration illustrated in FIG. 4bis suitable for rotating the polarization plane of plane polarized light from a first to a second orientation where the first and second orientations are both at 45° to the horizontal or vertical. The configuration illustrated in FIG. 4cis such that the slow and fast directions of half-wave plate186 are disposed at 45° to the horizontal and vertical when theswitch180 is in its “on” position. The configuration illustrated in FIG. 4cis suitable for rotating the polarization plane of plane polarized light from horizontal to vertical or vice versa.

FIGS. 5aand5billustrate a third and a fourth preferred embodiment of optical switches in accordance with the present invention. These embodiments are 1×4 optical switches, each comprising a cascaded arrangement of a set of bimorphic piezoelectric apparatuses in accordance with the present invention. Both the parallel cascaded 1×4optical switch500 of FIG. 5aand the serial cascaded 1×4optical switch550 of FIG. 5bcomprise a single inputoptical fiber502 disposed adjacent to acollimating lens503 and a set of four output optical fibers504a-504d, each of which is disposed adjacent to its own focusing lens505a-505d, respectively. It is to be kept in mind, however, that the illustrated optical pathways in eitherswitch500 or switch550 may be reversed so as to comprise a 4×1 optical switch with four input fibers504a-504dand asingle output fiber502. In switch500 (FIG. 5a), three bimorphic piezoelectric deflection/latchingapparatuses150a-150cin accordance with the present invention are disposed adjacent to one another so that the optical signal or beam pathways506a-506dcross the positions of theapparatuses150a-150cin sequence and either pass by each apparatus in a straight line or are deflected depending upon whether the apparatus is in its “off” or “on” position, respectively. In switch550 (FIG. 5b), two bimorphic piezoelectric deflection/latchingapparatuses150d-150ein accordance with the present invention are disposed similarly.

For instance, in FIG. 5a, an optical beam or signal508 is output fromfiber502 and, after being collimated bylens503, initially followspath segment506a, which crosses the position of first deflection/latching apparatus150a. Depending upon whetherapparatus150ais in the “off” or “on” state, signal508 either passes the position ofapparatus150aundeflected, thereby remaining onpath506a, or else is deflected ontopath506b, respectively. Thepath506aand thepath506bcontinue on so as to cross the positions of deflection/latchingapparatuses150cand150b, respectively. Ifapparatus150ais “off”, then, depending upon whetherapparatus150cis in the “off” or “on” state, signal508 either continues on alongpath506aso as to be focused bylens505aintofiber504aor else is deflected ontopath506cso as to be focused bylens505cintofiber504c, respectively. Likewise, ifapparatus150ais “on”, then, depending upon whetherapparatus150bis in the “off” or “on” state, signal508 either continues on alongpath506bso as to be focused bylens505bintofiber504bor else is deflected ontopath506dso as to be focused bylens505dintofiber504d, respectively. By this means, theapparatus500 functions as a 1×4 optical switch.

In the 1×4switch550, only two deflection and latching apparatuses,150d-150eare utilized. Theprism106eofapparatus150eis larger and formed with a wider apex angle than that of theprism106dofapparatus150d. Theapparatus150deither passesoptical signal512 straight through alongoptical path510awithout deflection, or else deflects it ontopath510bdepending upon the state of apparatus100d. Bothoptical pathways510aand510bare subsequently intercepted by theprism106ecomprising deflection/latching apparatus150e. Depending upon whether deflection/latching apparatus150eis “off” or “on”, it respectively either passes signal512 straight through along one of thepaths504aor504bwithout deflection, or else deflects signal512 onto one of thepaths504cor504d. Thesignal512 is then focused by one of the lenses505a-505dinto one of the output fibers504a-504d. By this means, theapparatus550 functions as a 1×4 optical switch.

Either of the switch embodiments illustrated in FIGS. 5aand5bmay be expanded to a greater number of output ports by adding more deflection and latching apparatuses in accordance with the present invention in either the parallel cascade (FIG. 5a) or the serial cascade (FIG. 5b) arrangement. Moreover, the separate deflection and latching apparatuses comprising either theswitch500 or theswitch550 may be disposed to as to cause successive signal deflections about respective axes that are not parallel to one another. This latter arrangement produces a switch capable of directing signals to outputs disposed within three dimensions, thereby saving space and increasing usage flexibility. Theswitch550 has the advantage overswitch500 of utilizing fewer components, thereby facilitating alignment and fabrication ease, and producing the advantage of compactness. However, theswitch500 has the potential advantage overswitch550 of not requiring ever-larger deflection prisms for the second and subsequent deflection/latching apparatuses of which it is comprised.

FIGS. 6aand6brespectively show a side view and a top view of a preferred embodiment of a reversibleoptical circulator600 which utilizes the differential phase retardance switch180 in accordance with the present invention to switch optical circulation between logical “clockwise” and “counterclockwise” directions. In the reversibleoptical circulator600 shown in FIGS. 6aand6b,reference numeral615 is a ferrule andreference numerals601,602,603 and604 are four optical ports contained within or secured byferrule615. Preferably, such optical ports comprise optical fibers although they may comprise any type or combination of types of optical inputting and outputting device, such as windows.

FIG. 7 shows an end view of the configuration of the four ports—Port A601,Port B602,Port C603 andPort D604—as viewed from the left side of thedevice600 of FIGS. 6aand6b. As also shown in FIGS. 6aand6b, four collimator lenses605-608 are disposed at the end offerrule615 such that each collimator receives light from and directs light to exactly one of the ports, specificallyPort601,602,603 and604, respectively. Collimated light rays emanating from any of these four ports601-604 are parallel to one another and define the direction of the main axis ofreversible circulator600.

In this specification, the positive or forward direction of the main axis of thereversible circulator600 is defined as extending from left to right as viewed in either FIG. 6aor6b. Consequently, as used in this document, the term “emanating from” refers to light or signal propagation along the positive main axis, from left to right, ofcirculator600, and the term “destined for” refers to light propagation in the reverse direction, from right to left, along the negative direction of the main axis of thecirculator600.

Disposed adjacent to the end offerrule615 is a first birefringent walk-off plate609 which has the property of separating any signal light ray emanating from any of the ports601-604 into two physically separated linearly polarized sub-signal rays—one innermost and one outermost sub-signal ray. This separation of signals into sub-signals is accomplished by deflection or offset of the path of one—the e-ray—of each pair of sub-signals in a first direction perpendicular to the circulator main axis. Because four ports exist, eight separate sub-signals are so defined and are comprised of four outermost and four innermost sub-signals. The outermost and innermost sub-signals from bothPort A601 andPort B602 comprise e-rays and o-rays, respectively, in their traverse throughbirefringent plate609. Conversely, the outermost and innermost sub-signals from bothPort C603 andPort D604 comprise o-rays and e-rays, respectively, in their traverse throughbirefringent plate609.

Disposed adjacent to the firstbirefringent plate609 and on the side ofplate609 opposite to ferrule615 are both a first610 and a second611 optical rotator, respectively. These two optical rotators,610 and611, have the property of rotating the orientation of the plane of polarized light passing therethrough by 90° around or about the light propagation direction. In the preferred embodiment, bothoptical rotators610 and611 comprise half wave plates, although either or both may comprise some other type of optically active element such as a liquid crystal device.Optical rotator610 is disposed so as to intercept only the two outermost sub-signals arising from or destined forPort A601 andPort B602. Likewise,optical rotator611 is disposed so as to intercept only the two outermost sub-signals arising from or destined forPort C603 andPort D604.

A second birefringent walk-off plate612 is disposed adjacent to the two reciprocaloptical rotators610 and611 on the side opposite to the firstbirefringent plate609. The thickness and optical orientation ofbirefringent plate612 are chosen so as to provide an offset in the first direction of one of the rays propagating therethrough by a distance equivalent to the common center-to-center inter-port separation distance.

A pair of 45° optical polarization rotation elements—a reciprocaloptical rotator616 and a non-reciprocal optical rotator617—are disposed to the side of the second birefringent walk-off plate612 opposite to the 90°optical rotators610 and611. As shown in FIG. 6b, the reciprocaloptical rotator616 is disposed so as to intercept all and only those sub-signal light rays either emanating from or destined forPort A601 andPort C603. The polarization plane direction of linearly polarized light of sub-signals propagating through reciprocaloptical rotator616 is reversibly rotated by 45° in the clockwise (CW) direction. The non-reciprocal optical rotator617 is disposed so as to intercept all and only those sub-signal light rays either emanating from or destined forPort B602 andPort D604. The polarization plane direction of linearly polarized light of sub-signals propagating through non-reciprocal optical rotator617 is non-reversibly rotated by 45° in the counter-clockwise (CCW) direction.

A switchable 90°optical rotation element618 is disposed to the side of either the reciprocaloptical rotator616 or the non-reciprocal optical rotator617 opposite to that of theplate612. The switchable 90°optical rotation element618 is controlled so as to rotate or not rotate the polarization plane of all light either emanating from or destined for exactly two of the optical ports. If, as in the example illustrated in FIG. 6b, theswitchable rotation element618 is disposed adjacent to non-reciprocal rotator617, then theswitchable rotation element618 can rotate the polarization plane of all and only those sub-signal light rays either emanating from or destined forPort B602 andPort D604. If, on the other hand, theswitchable rotation element618 is disposed adjacent toreciprocal rotator616, then theswitchable rotation element618 is capable of rotating the polarization plane of all and only those sub-signal light rays either emanating from or destined forPort A601 andPort C603.

A lens orlens assembly613 is disposed to the side ofelement618 opposite torotation elements616 and617. Finally, amirror614 is disposed at the focal point oflens613 opposite to the rotation elements616-618.

The two states of switchable 90°optical rotation element618 comprise a first state in which the orientation of the plane of polarized light either emanating from or destined for the two ports in question is rotated by 90° and a second state in which the orientation is not rotated. In the preferred embodiment of the present invention, the switchable 90°optical rotation element618 comprises thehalf wave plate186 of a differentialphase retardance switch180, as shown in FIG. 4a. FIG. 6cshows an end view of thecirculator600 illustrating the disposition ofelement618 in relation to the differentialphase retardance switch180 and a few other selected components ofreversible circulator600. In the preferred embodiment ofreversible circulator600, the first and second state of switchable 90°optical rotation element618 respectively correspond to the situation in which theelement618 is disposed so as to not intercept and so as to intercept optical ray paths emanating from or destined for the two ports in question. As further illustrated in FIG. 6c, the two states ofelement618 are controlled by the latching state ofswitch180 and the fast and slow optical orientations of the waveplate comprising element618 are disposed horizontal and vertical or vice versa. In an alternative embodiment, the two-state 90°optical rotation element618 may comprise a liquid crystal device, wherein the two polarizing states of the liquid crystal device are controlled by a voltage applied across the device.

As used in this specification, the terms “reciprocal optical rotator” or equivalently “reversible optical rotator” or “reciprocally rotating optical element” refer to optical components having the property such that the direction of rotation about the axis of light propagation, either clockwise (CW) or counter-clockwise (CCW), of the plane of polarization of linearly polarized light propagated therethrough is always the same when viewed facing the rotator towards the side at which the linearly polarized light beam enters the component. Conversely, the terms “non-reciprocal optical rotator” or equivalently “non-reversible optical rotator” or “non reciprocally rotating optical element” refer to optical components having the property such that the direction of rotation about the axis of light propagation, either clockwise (CW) or counter-clockwise (CCW), of the plane of polarization of linearly polarized light propagated therethrough is always the same when viewed facing the rotator from a fixed reference point in a fixed direction, regardless of the propagation direction of the light ray through the element. Non-reciprocal rotators typically comprise Faraday rotators, which rotate polarization planes of polarized light passing therethrough in response to or under the influence of an external magnetic field. A magnet or magnets in close proximity to the Faraday rotator usually produce the external magnetic field. In the case in which the non-reciprocal rotator617 comprises a Faraday rotator, theoptical circulator600 also comprises such magnets but, for clarity, these magnets are not shown in FIGS. 6a-6c.

The operation ofcirculator600 is described herein below with reference to FIG.8 and FIG.9. FIGS. 8 and 9 are both sequences of cross sections through thereversible circulator600 illustrating the locations and polarization states of port images created by the light of signals and sub-signals propagating therethrough in accordance with the present invention. The cross sections of FIG. 8 represent operation of thereversible circulator600 in which the switchable 90°optical rotation element618 is in its first, “off,” or no-rotation state. Conversely, the cross sections of FIG. 9 represent operation of thereversible circulator600 in which the switchable 90°optical rotation element618 is in its second or 90°-rotation state.

The cross-sections of FIGS. 8-9 are all drawn as viewed from the left side of thedevice600 of FIGS. 6aand6band are taken at the labeled cross-sectional planes U-U′, V-V′, W-W′, X-X′, and Y-Y′. These cross-sections correspond to locations similarly labeled on FIGS. 6aand6b. In the cross sections of FIGS. 8-9, the centers of labeled circles denote the positions of port images created by sub-signals propagating throughcirculator600 as projected onto the respective cross section. Concentric circles of different sizes indicate overlapping or co-propagating sub-signals. The sizes of these circles in the diagrams of FIGS. 8-9 have no physical significance. Barbs on the circles of FIGS. 8-9 indicate the orientations of polarization planes of the linearly polarized sub-signals that the respective circles represent. Circles with two pairs of barbs represent unpolarized or randomly polarized light or else superimposition of two lights with differing linear polarization orientations. A cross (“+”) in each cross-section of FIGS. 8-9 represents the projection of the center of thelens613 onto the cross section along a line parallel to the circulator main axis.

As will be evident from the discussion following, all sub-signal light is reflected by themirror614 of thereversible circulator600 so as to make one complete forward and one complete return traverse throughreversible circulator600. Therefore, each cross-section of sub-signal port images is shown twice, one time labeled with capital letters to denote forward propagation (FIGS. 8-9, upper rows) along the positive direction of the circulator main axis and one time labeled with small letters (FIGS. 8-9, lower rows) to denote reverse propagation along the negative direction of the circulator main axis. Heavy arrows indicate the sequence of images produced by light signals propagating through thereversible circulator600.

The paths of signals and sub-signals propagating throughreversible circulator600 in its first state are now described with reference to FIG.8. As seen in cross section U-U′800 of FIG. 8, signals emanating from each of the four ports—Port A601,Port B602,Port C603 andPort D604—are comprised of unpolarized light. After emanating from one of the four ports and passing through one of the collimator lenses605-608, signal light enters and passes through the firstbirefringent plate609 which separates it into physically separated horizontally and vertically polarized sub-signal components. In FIG. 8,sub-signal A810,sub-signal B812,sub-signal C814 andsub-signal D816 represent the images of horizontally polarized sub-signal light emanating, respectively, fromPort A601,Port B602,Port C603 andPort D604. Likewise, sub-signal A′811, sub-signal B′813, sub-signal C′815 and sub-signal D′817 represent the images of vertically polarized sub-signal light emanating, respectively, fromPort A601,Port B602,Port C603 andPort D604. It is to be noted the terms “vertical” and “horizontal” are used in this specification in a relative sense only and do not necessarily imply any particular spatial orientation of the referred-to apparatus or component.

The four vertically polarized sub-signals A′811, B′813, C′815 and D′817 all comprise e-rays during their traverse through the firstbirefringent plate609. Therefore, as shown in cross-section V-V′801, sub-signals811,813,815 and817 are all shifted in the first direction with respect to the corresponding horizontally polarized sub-signals810,812,814 and816, respectively. After passing through the firstbirefringent plate609, the four outermost sub-signals A′811, B′813,C814 andD816 pass through one of the two 90° optical rotators,610 and611, and therefore their light rays incur 90° rotations of the orientations of their polarization planes. Thus, as shown in cross section W-W′802, the polarization plane directions of sub-signals A′811 and B′813 change from vertical to horizontal while those ofsub-signals C814 andD816 change from horizontal to vertical.

After passing the positions of the reciprocaloptical rotators610 and611, all sub-signals enter and pass through the second birefringent walk-off plate612. The four vertically polarized sub-signals C′815, D′817,C814 andD816 traversebirefringent plate612 as e-rays and are thus deflected in the first direction while the four horizontally polarized sub-signals A′811, B′813, A810 andB812 traversebirefringent plate612 as undeflected o-rays. The optical orientation and thickness ofbirefringent plate612 are chosen such that the lateral deflection of e-rays upon traversing therethrough is exactly equal to the center-to-center inter-port separation distance. For this reason, after passing throughbirefringent plate612, the two sub-signal images C′815 andC814 become superimposed on the sub-signal images A′811 and A810, respectively and the two sub-signal images D′817 andD816 become superimposed on the sub-signal images B′813 andB812, respectively. Furthermore, the two sub-signals comprising each pair of superimposed sub-signals each follow identical paths until later separated during their return paths. This superimposition of sub-signals is shown in cross section X-X′803 of FIG.8.

After exitingplate612, each pair of superimposed sub-signals, A′811 and C′815, A810 andC814, B′813 and D′817, andB812 andD816 each travels along its own path with the two sub-signals comprising each pair remaining superimposed, one upon the other. The two pairs of sub-signals A′811 and C′815 and A610 andC614, which comprise all and only that light originating from Port A and Port C, pass through the 45° reciprocaloptical rotator616. In passing through reciprocaloptical rotator616, the polarization plane directions of light comprising these four sub-signals are all rotated by an angle of 45° CW around or about their propagation directions. The two pairs of sub-signals B′813 and D′817 andB812 andD816, which comprise all and only that light originating from Port B and Port D, pass through the non-reciprocal optical rotator617. In passing through non-reciprocal optical rotator617, the polarization plane directions of light comprising these four sub-signals are all rotated by an angle of 45° CCW around or about their propagation directions. Barbs in cross section Y-Y′804 show the orientations of the polarization planes of light of the various sub-signals after exitingelements816 and817.

The four pairs of sub-signals travel to and through thelens613, which brings them all to a common focal point atmirror614. Themirror614 immediately reflects all sub-signals back along their return paths throughcirculator600. Because the focal point of thelens613 is on the plane ofmirror614, the four pairs of sub-signals immediately diverge from one another after being reflected by themirror614 and pass through lens613 a second time in the reverse direction. The diverging pathways of the four pairs of returning sub-signals are set once again parallel to one another bylens613. Because the projection of the center oflens613 onto cross-section Y-Y′804 is centrally located between the four pairs of port images and because the focal point oflens613 is onmirror614, the four pairs of sub-signals are directed back towards reciprocaloptical rotator616 and non-reciprocal optical rotator617 along pathways which exactly superimpose upon those of forward propagating pairs of sub-signals.

Cross section y-y′805 shows the locations of the pairs of superimposed sub-signal images at their points of return entry into reciprocaloptical rotator616 and non-reciprocal optical rotator617. The focusing and re-collimation of sub-signal images bylens613 causes the inversion of image positions about the center of the lens as projected onto cross-section y-y′805. This inversion causes interchange of the positions of opposing pairs of sub-signals as projected onto cross-section y-y′805. Thus, upon re-entry into either reciprocaloptical rotator616 or non-reciprocal optical rotator617, as shown in cross-section y-y′805, the location of the returning pair ofsub-signal images B812 andD816 is the same as that of the forward propagating pair of sub-signals A′811 and C′815. Likewise, in cross-section y-y′805, the locations of returning pairs ofsub-signals A810 andC814, B′813 and D′817, and A′811 and C′815 are identical to those of forward propagating pairs of sub-signals B′813 and D′817, A810 andC814, andB812 andD816, respectively.

Because of the inversion properties oflens613, each of the returning sub-signals withinreversible circulator600 encounters an optical rotation element—either the reciprocaloptical rotator616 or the non-reciprocal optical rotator617—through which it did not pass during its forward path throughreversible circulator600. Thus, after passing throughlens613 on their return traverse throughreversible circulator600, thesub-signals B812, B′813,D816 and D′817 all pass through reciprocaloptical rotator616 and thus their light rays incur 45° CW rotations of the directions of their polarization planes. Because reciprocaloptical rotator616 is a reversible optical rotator and the sub-signal propagation in question is in the return direction, this rotation has an apparent CCW direction as viewed from the left side of thedevice600 and as indicated in FIG.8. Thesub-signals A810, A′811,C814 and C′815 all pass through non-reciprocal optical rotator617 and thus their light rays incur 45° CCW rotations of the directions of their polarization planes after passing throughlens613 on their return traverse throughreversible circulator600. Because non-reciprocal optical rotator617 is a non-reversible optical rotator, the rotation of the polarization planes of sub-signals passing therethrough is always in the CCW direction as viewed from the left side of thedevice600. The polarization state of each of the sub-signals after passing through either reciprocaloptical rotator616 or non-reciprocal optical rotator617 in the return direction is therefore either horizontal or vertical as indicated in cross section x-x′806 of FIG.8. With thecirculator600 in its first state, as shown in FIG. 8, theoptical rotation element618 causes no additional polarization plane rotation of sub-signals passing between cross section y-y′805 and cross section x-x′.

During return passage through the secondbirefringent plate612, the vertically polarizedsub-signals B812,C814, B′813 and C′815 pass therethrough as deflected e-rays while the horizontally polarizedsub-signals D816, A810, D′817 and A′811 pass therethrough as undeflected o-rays. For this reason, the two sub-signals comprising each pair of superimposed sub-signals become re-separated one from another upon passing through birefringent plate612 a second time. The deflection ofsub-signals B812,C814, B′813 and C′815 upon their second traverse throughbirefringent plate612 is exactly equal and opposite to the deflection of sub-signals C′815, D′817,C814, andD816 and during their first traverse through thisplate612. Therefore, the locations of the images of the various sub-signals after the second traverse of these sub-signals throughbirefringent plate612 are as shown in cross section w-w′807 of FIG.8.

After exiting the secondbirefringent plate612, the outermost returningsub-signals D816, A810, B′813 and C′815 pass through one of the two 90° optical rotators,610 and611, and therefore their light rays incur 90° rotations of the orientations of their polarization planes. As a result of these rotations, the polarization plane directions of light ofsub-signals D816 and A810 become vertical and those of the light of sub-signals B′813 and C′815 become horizontal. The positions and polarization states of the various sub-signals are thus as shown in cross section v-v′808 after passing, in the return direction, the positions of the 90° reciprocal optical rotators,610 and611.

Finally, all sub-signals enter the first birefringent walk-off plate609 in the return direction. The vertically polarizedsub-signals D816, A810,B812 andC814 pass throughplate609 as deflected e-rays whilst the horizontally polarized sub-signals D′817, A′811, B′813 and C′815 pass throughplate609 as undeflected o-rays. The deflection ofsub-signals D816, A810,B812 andC814 during return passage throughplate609 is exactly equal and opposite to the deflection of sub-signals A′811, B′813, C′815 and D′817 during their forward passage through thisplate609. Therefore, the vertically and horizontally polarized pairs ofsub-signals A810 and A′811,B812 and B′813,C814 and C′815, andD816 and D′817 become recombined at the positions of the collimator lenses605-608. Each of the collimator lenses focuses the return-path signal impinging thereon into the immediately adjacent port. As shown in cross section u-u′809, therefore, the recombined signals are located such that the signals originally from Port A, from Port B, from Port C and from Port D are directed into Port B, Port C, Port D and Port A, respectively. In this fashion, whenreversible circulator600 is in its first or “off” state, it functions as a logical “clockwise” optical circulator.

FIG. 9 illustrates the operation ofreversible circulator600 in its second or “on” state. In this first state, the switchable 90°optical rotation element618 imposes a 90° rotation upon the polarization plane orientation of plane polarized light passing therethrough. The manifestation of this 90° rotation is illustrated in the sequence of cross sections903-904 and in the sequence of cross sections905-906 in FIG.9. In passing from cross section X-X′903 to Y-Y′904, thesub-signals B812, B′813,D816 and D′817 all pass through the non-reciprocal optical rotator617 as well as through switchable 90°optical rotation element618. The polarization planes of these four sub-signals are first rotated 45° CCW by non-reciprocal optical rotator617 and then rotated an additional 90° byelement618. The net effect of these two rotations in sequence is equivalent to a 45° CW rotation of the polarization planes ofsub-signals B812, B′813,D816 and D′817 between cross section X-X′903 and cross section Y-Y′904. The polarization plane orientation of light ofsub-signals A810, A′811,C814 and C′815 only undergoes a single 45° CW rotation from passage through reciprocaloptical rotator616 as previously described in the discussion to FIG.8.

In passing from cross section y-y′905 to x-x′906, thesub-signals A810, A′811,C814 and C′815 all pass through the switchable 90°optical rotation element618 followed by the non-reciprocal optical rotator617. Thus, the polarization planes of these four sub-signals are first rotated by 90° byelement618 and then rotated an additional 45° CCW (as viewed from the left side of FIGS. 6aand6baccording to the convention of FIGS. 8-9) by element617. The net effect of these two rotations in sequence is equivalent to a 45° CW rotation (as viewed from the left of FIGS. 6a-6b) of the polarization planes ofsub-signals A810, A′811,C814 and C′ between cross section y-y′905 and cross section x-x′906.

Each of the sub-signals810-817 incurs an additional 90° rotation of its polarization plane orientation whenreversible circulator600 is in its second or “on” state relative to the situation in whichreversible circulator600 in its first or “off” state. This additional 90° rotation is illustrated by comparison ofcross sections907,908 and909 withcross sections807,808 and809, respectively. Because of this additional 90° rotation in the “on” state ofreversible circulator600, the identities of o-rays and e-rays are interchanged from those in the “off” state during the return passage of sub-signals through secondbirefringent plate612. Thus, in the “on” state, the paths ofsub-signals D816, A810, D′817 and A′811 are deflected during the return passage through second birefringent plate612 (FIG.9), but, in the “off” state, those ofB812,C814, B′813 and C′815 are instead deflected (FIG.8). As a final result, withreversible circulator600 in the first or “on” state, the light signals from Port A, Port B, Port C and Port D are respectively directed to Port D, Port A, Port B and Port C. Thus, in this fashion, whenreversible circulator600 is in its second or “on” state, it functions as a logical “counterclockwise” optical circulator.

FIG. 10aillustrates the operation of a conventional four-portoptical circulator1000. In thecirculator1000, light input toPort A1002 is output fromPort B1004, light input toPort B1004 is output fromPort C1006, light input toPort C1006 is output fromPort D1006 and light input toPort D1008 is output fromPort A1002. This operation is termed herein as “clockwise” optical circulation.

By contrast, FIG. 10billustrates the operation of the preferred embodiment of the reversibleoptical circulator600 in accordance with the present invention. In its “off” state, thereversible circulator600 operates with “clockwise” optical circulation. However, in its “on” state, thereversible circulator600 operates with “counterclockwise” optical circulation, which is exactly opposite to “clockwise” circulation. The “clockwise” or “counterclockwise” state ofreversible circulator600 is controlled by the state of the switchable 90°optical rotation element618. When switchable 90°optical rotation element618 is in its “on” state such that there is effected a 90° rotation of the polarization plane of plane polarized light passing therethrough or there-past, thenreversible circulator600 operates in the “counterclockwise” state. However, when switchable 90°optical rotation element618 is in its “off” state such that there is no polarization plane rotation of plane polarized light passing therethrough or there-past, then the operation ofreversible circulator600 is “clockwise”. When the switchable 90°optical rotation element618 comprises the half-wave plate of a differential phase retardance switch180 in accordance with the present invention, then thereversible circulator600 can be switched between its two circulatory states in approximately one millisecond.

FIGS. 11aand11bare side and top views, respectively, of a preferred embodiment of a switchable optical channel separator in accordance with the present invention which utilizes the differentialphase retardance switch180. Most of the components comprising the switchableoptical channel separator1100 illustrated in FIGS. 11a-11bare identical in type and disposition to their counterparts in thereversible circulator600 and are therefore numbered similarly to those counterparts as shown in FIGS. 6aand6b. However, the switchableoptical channel separator1100 does not comprise thereciprocal rotator616 or the non-reciprocal rotator617, and comprises anon-linear interferometer1114 in place of themirror614. The switching capability of switchableoptical channel separator1100 is derived from the operation of the switchable 90°optical rotation element618 which, in the preferred embodiment, comprises the half-wave plate of a differential phase retardance switch180 of the present invention, as is illustrated in FIG. 11c.

Thenon-linear interferometer1114 is an instance of an invention disclosed in a co-pending U.S. Patent Application, incorporated herein by reference, entitled “Nonlinear Interferometer for Fiber Optic Wavelength Division Multiplexer Utilizing a Phase Differential Method of Wavelength Separation,” Ser. No. 09/247,253, filed on Feb. 10, 1999, and also in a second co-pending U.S. Patent Application, also incorporated herein by reference, entitled “Dense Wavelength Division Multiplexer Utilizing an Asymmetric Pass Band Interferometer”, Ser. No. 09/388,350 filed on Sep. 1, 1999. Thenon-linear interferometer1114 has the property such that, if the light beam reflected therefrom is an optical signal comprised of a plurality of channels and the light of each channel is linearly polarized, then the light of every member of a second set of channels is reflected with a 90° rotation of its polarization plane direction while the light of every member of a first set of channels, wherein the first and second channel sets are interleaved with one another, is reflected with unchanged polarization. In the following discussion, the channels whose light rays experience the 90° polarization-plane rotation upon interaction withnon-linear interferometer1114 are arbitrarily referred to as “even” channels and the remaining channels are referred to as “odd” channels. The patent application with Ser. No. 09/247,253 teaches the operation of an interferometer in which all channels have identical channel spacings and channel band widths. The patent application with Ser. No. 09/388,350 teaches the operation of an interferometer in which the channel bandwidths of the first interleaved set of channels are not the same as those of the second interleaved set of channels and the channel spacing is not uniform.

FIGS. 12-15 illustrate the operation of the switchableoptical channel separator1100 and, similarly to FIGS. 8-9, comprise sequences of cross sections throughseparator1100 illustrating the locations and polarization states of fiber images. FIGS. 12 and 13 illustrate the propagation of signals of odd and even channels, respectively, through theseparator1100 in its first state. This first state is such that the switchable 90°optical rotation element618 does not rotate the polarization plane of polarized light passing therethrough. FIGS. 14 and 15 illustrate the propagation of signals of odd and even channels, respectively, through theseparator1100 in its second state. This second state is such that the switchable 90°optical rotation element618 rotates the polarization plane of polarized light passing therethrough.

The basic principles of operation ofchannel separator1100, as illustrated in FIGS. 12-15, are similar to those of thereversible circulator600, as previously illustrated in FIGS. 8-9, and are not repeated here. However, it is to be kept in mind that, in FIGS. 12 and 13, the switchable 90°optical rotation element618 is not disposed so as to rotate signal light polarization and thus the two members of each of the pairs of cross sections1203-1204 and1205-1206 (FIG.12), or the pairs of cross sections1303-1304 and1305-1306 (FIG. 13) are identical. Furthermore, in FIGS. 14 and 15, the switchable 90°optical rotation element618 is disposed so as to rotate by 90° the light polarization planes of signals disposed to the right side of the appropriate cross sections. The effects of these rotations are seen by comparison of the pairs of cross sections1403-1404 and1405-1406 (FIG.14), or the pairs of cross sections1503-1504 and1505-1506 (FIG.15). It is also to be kept in mind that, in FIG.13 and FIG. 15, the polarization planes of even-channel signals are rotated by 90° betweencross section1304 and cross section1305 (FIG. 13) and also betweencross section1504 and1505 (FIG.15). The effect of each such rotation of signal light polarization is propagated along the remainder of the optical path until the signal is outputted from thechannel separator1100 through one of its four input and output ports.

FIGS. 16aand16brespectively depict the two operational states of the switchableoptical channel separator1100 in accordance the present invention. In the first such operational state illustrated in FIG. 16a, a first set of wavelengths consonant with a first set of interleaved channels are routed from Port A to Port B and from Port C to Port D and a second set of wavelengths consonant with a second set of interleaved channels are routed from Port A to Port D and from Port C to Port B. For convenience, the first and second sets of interleaved channels are herein termed “odd” and “even” channels, respectively.

For instance, if a set of n wavelength-division multiplexed channels denoted by λ₁, λ₂, λ₃, . . . , λ_nare input to Port A of the switchable optical channel separator1100 in its first operational state, then the first or “odd” channels λ₁, λ₃, λ₅, . . . are routed to Port B and the second or “even” channels λ₂, λ₄, λ₆, . . . are routed to Port D. Similarly, if a second set of n wavelength-division multiplexed channels denoted by λ′₁, λ′₂, λ′₃, . . . , λ′_nare input to Port C of the switchable optical channel separator1100 in the same first operational state, then the first or “odd” channels λ′₁, λ′₃, λ′₅, . . . are routed to Port D and the second or “even” channels λ′₂, λ′₄, λ′₆, . . . are routed to Port B. Thus, with the switchable optical channel separator1100 in its first operational state, the output at Port B comprises the odd channels λ₁, λ₃, λ₅, . . . originally from Port A multiplexed together with the even channels λ′₂, λ′₄, λ′₆, . . . originally from Port C, and the output at Port D comprises the odd channels λ′₁, λ′₃, λ′₅, . . . originally from Port C multiplexed together with the even channels λ₂, λ₄, λ₆, . . . originally from Port A. The channel separator operates similarly in the reverse direction—that is, when Ports B and D are utilized for input and Ports A and C are utilized for output. In other words, the path of each and every channel is reversible.

In FIG. 16b, the switchableoptical channel separator1100 is illustrated in its second operational state. In this state, the output at Port B comprises the even channels λ₂, λ₄, λ₆, . . . originally from Port A multiplexed together with the odd channels λ′₁, λ′₃, λ′₅, . . . originally from Port C, and the output at Port D comprises the even channels λ′₂, λ′₄, λ′₆, . . . originally from Port C multiplexed together with the odd channels λ₁, λ₃, λ₅, . . . originally from Port A. The channel separator operates similarly in the reverse direction.

The operational state of switchableoptical channel separator1100 is controlled by the state of the switchable 90°optical rotation element618. When switchable 90°optical rotation element618 is in its “on” state such that there is effected a 90° rotation of the polarization plane of plane polarized light passing therethrough or there-past, then the switchableoptical channel separator1100 is in its second state. However, when switchable 90°optical rotation element618 is in its “off” state such that there is no polarization plane rotation of plane polarized light passing therethrough or there-past, then the switchableoptical channel separator1100 is in its first state. When the switchable 90°optical rotation element618 comprises the half-wave plate of a differential phase retardance switch180 of the present invention, then thechannel separator1100 can be switched between its two routing states in approximately one millisecond.

FIG. 17 is an illustration of a preferred embodiment of a self-switching opticalline restoration switch1700 in accordance with the present invention. Theswitch1700 utilizes a reversibleoptical circulator600 of the present invention. The reversibleoptical circulator600 is optically coupled to aninput telecommunications line1702, anoutput telecommunications line1704, anauxiliary telecommunications line1710, and adetector link1708 through its Port A, Port B, Port D and Port C, respectively. The detector link is optically coupled to a photo-detector1712 at its end oppositereversible circulator600. The photo-detector1712 is electrically coupled to the switchable 90°optical rotation element618 component (not shown) ofreversible circulator600 through an electrical orelectronic link1714. In normal operation, thereversible circulator600 of self-switching opticalline restoration switch1700 is in its “off” position, and thus signals input to Port A frominput line1702 are directed in the “clockwise” circulation direction to Port B and thence tooutput line1704. In this situation, theauxiliary telecommunications line1702 remains unused and no optical signal is directed to the photo-detector1712.

If there should be a line break withinoutput telecommunications line1704 and there is no optical isolator between thedevice1700 and the line break, then signals will be reflected at the break point and will propagate backwards throughline1704 back toreversible circulator600. These reflected signals and/or other lights will then be input toreversible circulator600 through its Port B. Since thereversible circulator600 will be in its “off” state immediately after such a line break occurs, these reflected signals and/or other lights will be directed in a “clockwise” circulation direction so as to be output from Port C to link1708 and thence to photo-detector1712. When photo-detector1712 senses the presence of the reflected signals or other lights, it sends an electrical or electronic signal, vialine1714, which is sufficient to switch the switchable 90°optical rotation element618 to its “on” state, thereby transformingreversible circulator600 into its “on” state. Once this switching has occurred, signals or other lights inputted to Port A frominput line1702 will be directed in a “counter-clockwise” circulatory direction to Port D and thence toauxiliary telecommunications line1710. In this fashion, the self-switching opticalline restoration switch1700 automatically switches signals and/or other lights away from the brokenprimary output line1704 and into theauxiliary line1710.

FIG. 18 is an illustration of a preferred embodiment of an optical cut-in orbypass switch1800 in accordance with the present invention. The cut-in orbypass switch1800 is suitable for automated insertion or removal of anetwork component1812 into or out of a telecommunications line. Theswitch1800 comprises a reversibleoptical circulator600 in accordance with the present invention respectively optically coupled to aninput telecommunications line1802 through its Port A, to anoutput telecommunications line1804 through its Port B, and to a first1808 and a second1810 optical link through its Port C and Port D. The optical links1808-1810 are each optically coupled to thenetwork component1812. Thenetwork component1812 may comprise any one or a combination of a variety of optical or electro-optical components such as optical filters, optical attenuators, optical amplifiers, optical add/drops, dispersion compensators, transponders, wavelength shifters, etc.

In a first or “off” state, thereversible circulator600 ofswitch1800 receives optical signal input frominput line1802 through its port A and re-directs this signal in a “clockwise” circulatory direction so as to be output from Port B tooutput line1804. In this state of operation, signals completely bypass thecomponent1812. In a second state of operation, thereversible circulator600 is placed in its “on” state such that signals input at Port A are re-directed in a “counter-clockwise” circulatory direction to Port D and thence to the secondoptical link1810 andnetwork component1812. Thenetwork component1812 performs one or more of signal conditioning, signal addition or signal deletion operations upon the signal or signals received from thesecond link1810 and then outputs the conditioned, modified or substituted signals to the firstoptical link1808. The signal(s) output fromcomponent1812 to thefirst link1808 need not be the same signal or signals received bycomponent1812 from thesecond link1810. The signals received by the firstoptical link1808 fromcomponent1812 are then delivered to Port C of thereversible circulator600 from which they are directed to Port B and subsequently output to theoutput line1804. In this fashion, the network component can be automatically switched in or out of an optical transmission within a millisecond as changing needs require.

Although the present invention has been described with an optical switching device utilizing a bi-morphic piezoelectric material, one of ordinary skill in the art will understand that other suitable materials may be used without departing from the spirit and scope of the present invention.

A method and apparatus for optical switching devices utilizing a bi-morphic piezoelectric electro-mechanical deflection and latching apparatus has been disclosed. The optical switching devices include a 1×2 optical switch utilizing a single electro-mechanical apparatus, various 1×N optical switches utilizing a plurality of electro-mechanical apparatus in a cascade arrangement, a reversible optical circulator, and a switchable optical channel separator. The optical devices in accordance with the present invention posseses the advantages of stable and reproducible operation, high switching speeds relative to other mechanical devices and low sensitivity to slight optical mis-alignments or vibrations. The optical devices in accordance with the present invention are of a compact modular design that allows the construction of more complex optical devices through utilization of a cascading arrangement, where an optical beam or signal can be deflected about axes in more than one spatial dimension.

Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.

Claims (15)

What is claimed is:

1. A reversible optical circulator, comprising:

a first port;

a second port; and

a third port, wherein in a first state, light input from the first port is output to the second port and light input from the second port is output to the third port,

wherein in a second state, light input from the third port is output to the second port and light input from the second port is output to the first port,

wherein the first state is switchable to the second state utilizing an optical switch comprising:

an arm comprising a piezoelectric material, the arm comprising a first and a second face and a first and a second end, wherein the first face is opposite to the second face, wherein the first end is opposite to the second end,

at least one electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm,

a support coupled to the first end of the arm for fixedly supporting the first end,

an object with a convex surface coupled to the second end of the arm,

a polarization rotation element coupled to the second face of the arm,

a first magnet proximately located to the object and to the first face of the arm, and

a second magnet proximately located to the object and to the second face of the arm.

2. The circulator ofclaim 1, wherein the arm comprises:

a first piezoelectric plate; and

a second piezoelectric plate coupled to the first piezoelectric plate in parallel.

3. The circulator ofclaim 2, wherein the at least one electrode comprises:

a first electrode located between the first and the second piezoelectric plates;

a second electrode coupled to the first piezoelectric plate at a side opposite to the first electrode; and

a third electrode coupled to the second piezoelectric plate at a side opposite to the first electrode.

4. The circulator ofclaim 1, wherein the support comprises:

a first support member coupled to the first end and the first face of the arm; and

a second support member coupled to the first end and the second face of the arm.

5. The circulator ofclaim 1, wherein the object comprises:

a first hemisphere coupled to the second end and the first face of the arm; and

a second hemisphere coupled to the second end and the second face of the arm.

6. An optical circulator, comprising:

a first birefringent plate for receiving at least one signal light ray from a first port, wherein the first birefringent plate separates the at least one signal light ray into a plurality of sub-signal rays;

a second birefringent plate optically coupled to the first birefringent plate;

at least one optical rotator optically coupled between the first and second birefringent plates, wherein the at least one optical rotator intercepts a portion of the plurality of sub-signal rays;

at least one reciprocal optical rotator and at least one non-reciprocal optical rotator optically coupled to the second birefringent plate at a side opposite to the at least one optical rotator;

an optical switch optically coupled to the at least one non-reciprocal optical rotator or the at least one reciprocal optical rotator at a side opposite to the second birefringent plate;

a lens optically coupled to the at least one reciprocal optical rotator or the at least one non-reciprocal optical rotator, and the optical switch at a side opposite to the second birefringent plate; and

a mirror optically coupled to the lens at a side opposite to the optical switch,

wherein the mirror reflects the plurality of sub-signal rays such that the plurality of sub-signal rays is folded back upon itself,

wherein the at least one reciprocal optical rotator, the optical switch, the at least one non-reciprocal optical rotator, the at least one optical rotator, and the first and second birefringent plates recombine the reflected plurality of sub-signal rays into the at least one signal light ray, such that the recombined at least one signal light ray is directed to a second port.

7. The circulator ofclaim 6, wherein the optical switch comprises:

an arm comprising a piezoelectric material, the arm comprising a first and a second face and a first and a second end, wherein the first face is opposite to the second face, wherein the first end is opposite to the second end;

at least one electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm;

a support coupled to the first end of the arm for fixedly supporting the first end;

an object with a convex surface coupled to the second end of the arm;

an optical element coupled to the second face of the arm capable of deflecting an optical signal traveling therethrough;

a first magnet proximately located to the object and to the first face of the arm; and

a second magnet proximately located to the object and to the second face of the arm.

8. The circulator ofclaim 7, wherein the arm comprises:

a first piezoelectric plate; and

a second piezoelectric plate coupled to the first piezoelectric plate in parallel.

9. The circulator ofclaim 8, wherein the at least one electrode comprises:

a first electrode located between the first and the second piezoelectric plates;

a second electrode coupled to the first piezoelectric plate at a side opposite to the first electrode; and

a third electrode coupled to the second piezoelectric plate at a side opposite to the first electrode.

10. The circulator ofclaim 7, wherein the support comprises:

a first support member coupled to the first end and the first face of the arm; and

a second support member coupled to the first end and the second face of the arm.

11. The circulator ofclaim 7, wherein the object comprises:

a first hemisphere coupled to the second end and the first face of the arm; and

a second hemisphere coupled to the second end and the second face of the arm.

12. The circulator ofclaim 7, wherein the optical element comprises a switchable 90 degree optical rotation element.

13. A system for directing a signal light ray, comprising:

an optical network, the optical network comprising the signal light ray; and

an optical circulator, comprising:

a first birefringent plate for receiving at least one signal light ray from a first port, wherein the first birefringent plate separates the at least one signal light ray into a plurality of sub-signal rays;

a second birefringent plate optically coupled to the first birefringent plate;

at least one optical rotator optically coupled between the first and second birefringent plates, wherein the at least one optical rotator intercepts a portion of the plurality of sub-signal rays;

at least one reciprocal optical rotator and at least one non-reciprocal optical rotator optically coupled to the second birefringent plate at a side opposite to the at least one optical rotator;

an optical switch optically coupled to either the at least one non-reciprocal optical rotator or the at least one non-reciprocal optical rotator at a side opposite to the second birefringent plate;

a lens optically coupled to the at least one reciprocal optical rotator or the non-reciprocal optical rotator, and the optical switch at a side opposite to the second birefringent plate; and

a mirror optically coupled to the lens at a side opposite to the optical switch,

wherein the mirror reflects the plurality of sub-signal rays such that the plurality of sub-signal rays is folded back upon itself,

wherein the at least one reciprocal optical rotator, the optical switch, the at least one non-reciprocal optical rotator, the at least one optical rotator, and the first and second birefringent plates recombine the reflected plurality of sub-signal rays into the at least one signal light ray, such that the recombined at least one signal light ray is directed to a second port.

14. The system ofclaim 13, wherein the optical switch comprises:

an arm comprising a piezoelectric material, the arm comprising a first and a second face and a first and a second end, wherein the first face is opposite to the second face, wherein the first end is opposite to the second end;

at least one electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm;

a support coupled to the first end of the arm for fixedly supporting the first end;

an object with a convex surface coupled to the second end of the arm;

an optical element coupled to the second face of the arm capable of deflecting an optical signal traveling therethrough;

a first magnet proximately located to the object and to the first face of the arm; and

a second magnet proximately located to the object and to the second face of the arm.

15. A method for directing a signal light ray, comprising the steps of:

(a) separating the signal light ray into a plurality of sub-signal rays, wherein the signal light ray is inputted from a first port;

(b) rotating a polarization direction of a portion of the plurality of sub-signal rays utilizing an optical switch comprising a switchable 90 degree rotation element, wherein the utilizing an optical switch comprising a switchable 90 degree rotation element, wherein the optical switch comprises:

an arm comprising a piezoelectric material, the arm comprising a first and a second face and a first and a second end, wherein the first face is opposite to the second face, wherein the first end is opposite to the second end,

at least one electrode coupled to the arm for providing a voltage difference between the first and second faces of the arm,

a support coupled to the first end of the arm for fixedly supporting the first end,

an object with a convex surface coupled to the second end of the arm,

an optical element coupled to the second face of the arm capable of deflecting an optical signal traveling therethrough,

a first magnet proximately located to the object and to the first face of the arm, and

a second magnet proximately located to the object and to the second face of the arm;

(c) reflecting the rotated portion and a remainder of the plurality of sub-signal rays, such that the rotated portion and the remainder are folded back upon themselves; and

(d) combining the rotated portion and the remainder of the plurality of sub-signal rays into the signal light ray, wherein the signal light ray is outputted to a second port.

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